1. Field of the Invention
The invention relates to a vehicle seat frame including a collar member, and relates also to a method of producing the collar member.
2. Description of Related Art
Some vehicle seat frames are provided with a lifter device configured to adjust the height of a seat cushion. As illustrated in FIG. 8 and FIG. 9, in a lifter device 100 described in Japanese Unexamined Patent Application Publication No. 2015-67136 (JP 2015-67136 A), a side frame 110 of a seat cushion, a front link 120, an upper rail 132 of a slide rail 130, and a rear link 140 constitute a four-bar linkage mechanism. A front lifter mechanism includes a collar 150 having a cylindrical portion 150a and a flange 150b. The cylindrical portion 150a of the collar 150 is passed through a through-hole of the front link 120 and secured to the front link 120 by welding. The outer peripheral surface of a portion of the cylindrical portion 150a of the collar 150, the portion being between the front link 120 and the flange 150b, is in contact with the peripheral surface defining a hole of the side frame 110 and is rotatably supported by the side frame 110. One end portion of a front pipe 160 having an outer diameter that is slightly smaller than the inner diameter of the collar 150 is inserted in the cylindrical portion 150a of the collar 150, and the outer peripheral surface of the front pipe 160 and the collar 150 are secured to each other by welding. A pinion gear 171 rotatably attached to the side frame 110 is meshed with a sector gear 172 coupled to the rear link 140. As the pinion gear 171 is rotated, the rear link 140 pivots in the front-rear direction about a shaft 133 attached to the upper rail 132, so that the side frame 110 moves up and down via the collar 150. At this time, the front link 120 moves in accordance with the movement of the rear link 140, so that the side frame 110 moves up and down while the side frame 110 is kept parallel to the slide rail 130.
Japanese Unexamined Patent Application Publication No. 2004-255405 (JP 2004-255405 A) describes a method of producing such a collar 150 by press working. According to this method, several deep drawing processes are sequentially performed on a flat steel sheet, so that a flange is formed while the diameter of a cylindrical portion is gradually reduced. Finally, a through-hole is formed in a bottom portion of the cylindrical portion. In this way, the collar 150 is produced.
In the technology described in JP 2015-67136 A, the outer diameter of an outer peripheral portion of the cylindrical portion 150a of the collar 150, which is in contact with the peripheral surface defining the hole of the side frame 110, and the inner diameter of an inner peripheral portion of the cylindrical portion 150a of the collar 150, which is in contact with the outer peripheral surface of the front pipe 160, are both formed to have high dimensional accuracy. The production method described in JP 2004-255405 A is employed to produce the collar 150. The production method achieves high dimensional accuracy of both the outer diameter and inner diameter of the cylindrical portion 150a. However, the production method requires at least four steps, and each step is time-consuming. This may increase the production cost.